Indeed it would be a bit earlier than 2140.Due to increasing difficulty, it takes less than 4 years to reach the first halving and the second halving is expected to happen in mid-2016 rather than 2017

You are assuming that difficulty will never decrease?

Of course theoretically it could decrease, but I can only see the hashrate to be level out, rather than going down significantly (unless bitcoin has completely died or be replaced someday).If the miners find mining not profitable, they would sell their equipment and the new owners will still use them on mining (maybe without understanding its profitability or maybe just mining for fun).

Of course theoretically it could decrease, but I can only see the hashrate to be level out, rather than going down significantly (unless bitcoin has completely died or be replaced someday).If the miners find mining not profitable, they would sell their equipment and the new owners will still use them on mining (maybe without understanding its profitability or maybe just mining for fun).

EDIT: Fixed typos.

You are aware that the difficulty dropped by nearly 10% on March 25, 2011, right?

Of course theoretically it could decrease, but I can only see the hashrate to be level out, rather than going down significantly (unless bitcoin has completely died or be replaced someday).If the miners find mining not profitable, they would sell their equipment and the new owners will still use them on mining (maybe without understanding its profitability or maybe just mining for fun).

EDIT: Fixed typos.

You are aware that the difficulty dropped by nearly 10% on March 25, 2011, right?

Yes, and indeed the difficulty has dropped by 18.03% on Oct 31 2011 and by 11.59% on Dec 26 2012. Maybe I should modify my earlier reply as "IMHO, it may be a bit earlier than 2140."